. The overall goal of this research is to understand the role of hnRNP A1 protein (A1) and other closely related hnRNP A/B proteins in pre-mRNA packaging and processing in the cell nucleus. The hnRNP A/B proteins are abundant, nuclear proteins which are highly conserved throughout metazoan evolution. Recent studies have demonstrated that these proteins promote the rapid annealing of complementary RNA strands, and play a role in splice site selection. These activities are important for the regulation of gene expression in eukaryotes. In collaboration with Drs. Adrian Krainer and Akila Mayeda at Cold Spring Harbor, the investigators will prepare a series of variant forms of A1 in order to identify regions within the individual domains of A1 which are essential for activity in alternative pre-mRNA splicing. Variant proteins will be characterized with respect to their RNA binding and RNA-RNA annealing properties. Selected proteins will then be used to study the requirements of A1 for site-specific binding and protein-facilitated annealing with different types of RNA substrates. These studies are important for understanding the interactions of A1 with pre mRNA and role of hnRNP A/B proteins in ribonucleoprotein assembly and pre-mRNA processing. The studies will also provide insight into the role of hnRNP A/B proteins in the regulation of alternative processing and export of processed mRNAs to the cytoplasm.